This invention relates to a motor control apparatus for controlling the start, rotation and stop of a motor.
As a motor control system for controlling the start, rotation and stop of a motor, particularly a DC motor, there is one as shown in FIG. 1. It includes a pulse generator 10 which supplies a signal CD to a motor control section 12 when a trigger signal A is applied. The motor control section 12 supplies a signal E to a motor 14 in response to the signal CD, whereby the motor 14 is rotated, for instance in the clockwise direction. A shaft 16 of the motor 14 carries a rotary disc 20 secured to it and provided with a cam 18. A leaf switch 22 which is provided near the periphery of the rotary disc 20 is on-off operated as the cam 18 is rotated in unison with the motor 14. As the switch 22 is on-off operated, a trigger signal B is fed back to the pulse generator 10. When the trigger signal B is fed back, the state of the signal CD is altered. As a result, the signal E supplied to the motor 14 is switched to a polarity with which it tends to stop the inertial rotation of the motor 14, for instance from the positive to negative polarity. With the appearance of this signal, the rotation of the motor 14 is stopped in a short period of time. The motor control system as described above finds applications in lieu of a plunger mechanism in mechanisms where a magnetic head of a tape recorder is brought into contact with or separated from a magnetic tape according to the rotational angle of the motor 14.
FIG. 2 shows an example of the circuit construction of the motor control section 12, and FIG. 3 is a timing chart illustrating the operation of the circuit of FIG. 2. When the trigger signal A is changed in logic level from "0" to "1" at an instant t10 as shown in A in FIG. 3, a first signal C which goes to the logic level "1" at the instant t10 is generated from the pulse generator 10 as shown in C in FIG. 3. In correspondence to this first signal C, a signal E1 is supplied from a motor driver 24 to the motor 14. More particularly, during the logic level "1" period of the first signal C (from instant t10 to instant t12), the signal E1 is supplied to the motor 14 to cause the rotation thereof, for instance in the clockwise direction. When the motor 14 is rotated for a predetermined rotational angle (about 360.degree. in FIG. 1), the switch 22 is turned off and on by the cam 18 at the instant t12, whereupon the trigger signal B is fed to the pulse generator 10. At this time, the first signal C goes back to the logic level "0" while a signal D goes to the logic level "1" as shown in C and D in FIG. 3 respectively. The signal D is supplied to a motor braking circuit 26. During the logic level "1" period of the signal D (from instant t12 to instant t14), the motor braking circuit 26 provides a signal E2 for stopping the inertial rotation of the motor 14. With this signal E2, the motor 14 is given a force tending to rotate it in the reverse direction and is thus quickly stopped. The period from the instant t10 to the instant t14 constitutes one start/stop cycle of the motor 14. With the construction of FIG. 2, however, means (10, 26) for forcibly stopping the motor 14 under the control of the switch 22 and signal D is required; otherwise, the rotor of the motor 14 will be allowed to continue the inertial rotation after the instant t14 in FIG. 3.
As is shown, according to the motor control system described above, means (18, 22) for providing the signals C and D for the two different lines and the trigger signal B are required. The provision of a plurality of signal paths and also the adoption of the means (18, 22) including mechanical contacts lead to the cost increase of the product utilizing such system and are also disadvantageous from the standpoint of reliability (faulty occurrence probability).